[OSPF] [Technical Errata Reported] RFC5709 (3585)

[RFC Errata System <[e-mail]>]

The following errata report has been submitted for RFC5709,
"OSPFv2 HMAC-SHA Cryptographic Authentication".

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You may review the report below and at:
http://www.rfc-editor.org/errata_search.php?rfc=5709&eid=3585

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Type: Technical
Reported by: Mike Dubrovsky <[e-mail]>

Section: 3.3

Original Text
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(1) PREPARATION OF KEY
       In this application, Ko is always L octets long.

       If the Authentication Key (K) is L octets long, then Ko is equal
       to K.  If the Authentication Key (K) is more than L octets long,
       then Ko is set to H(K).  If the Authentication Key (K) is less
       than L octets long, then Ko is set to the Authentication Key (K)
       with zeros appended to the end of the Authentication Key (K),
       such that Ko is L octets long.

Corrected Text
--------------
(1) PREPARATION OF KEY
       In this application, Ko is always B octets long and is computed as
       follows:

       If the Authentication Key (K) is B octets long, then Ko is equal
       to K.  If the Authentication Key (K) is more than B octets long,
       then Ko is set to H(K) and then appended with (B-L) zeroes to 
       create a B octets long string Ko.  If the Authentication Key (K) is
       less than B octets long, then Ko is set to the Authentication Key (K)
       with zeros appended to the end of the Authentication Key (K),
       such that Ko is B octets long.


Notes
-----
This is in accordance with RFC2104(HMAC: Keyed-Hashing for Message Authentication). Reproducing the relevant text below:

2. Definition of HMAC

The definition of HMAC requires a cryptographic hash function, which
we denote by H, and a secret key K. We assume H to be a cryptographic
hash function where data is hashed by iterating a basic compression
function on blocks of data. We denote by B the byte-length of such
blocks (B=64 for all the above mentioned examples of hash functions),
and by L the byte-length of hash outputs (L=16 for MD5, L=20 for
SHA-1). The authentication key K can be of any length up to B, the
block length of the hash function. Applications that use keys longer
than B bytes will first hash the key using H and then use the
resultant L byte string as the actual key to HMAC. In any case the
minimal recommended length for K is L bytes (as the hash output
length). See section 3 for more information on keys.


Also, according to FIPS PUB 198, section 5(HMAC SPECIFICATION) :

STEPS
STEP-BY-STEP DESCRIPTION
Step 1
If the length of K = B: set K0 = K. Go to step 4.
Step 2
If the length of K > B: hash K to obtain an L byte string, then append (B-L) zeros to create a B-byte string K0 (i.e., K0 = H(K) || 00...00). Go to step 4.
Step 3
If the length of K < B: append zeros to the end of K to create a B-byte string K0 (e.g., if K is 20 bytes in length and B = 64, then K will be appended with 44 zero bytes 0x00).
Step 4
Exclusive-Or K0 with ipad to produce a B-byte string: K0 ¯ ipad.
Step 5
Append the stream of data 'text' to the string resulting from step 4: (K0 ¯ ipad) || text.
Step 6
Apply H to the stream generated in step 5: H((K0 ¯ ipad) || text).
Step 7
Exclusive-Or K0 with opad: K0 ¯ opad.
Step 8
Append the result from step 6 to step 7: (K0 ¯ opad) || H((K0 ¯ ipad) || text).
Step 9
Apply H to the result from step 8: H((K0 ¯ opad )|| H((K0 &#65455; ipad) || text)).
Step 10
Select the leftmost t bytes of the result of step 9 as the MAC.

Instructions:
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RFC5709 (draft-ietf-ospf-hmac-sha-07)
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Title               : OSPFv2 HMAC-SHA Cryptographic Authentication
Publication Date    : October 2009
Author(s)           : M. Bhatia, V. Manral, M. Fanto, R. White, M. Barnes, T. Li, R. Atkinson
Category            : PROPOSED STANDARD
Source              : Open Shortest Path First IGP
Area                : Routing
Stream              : IETF
Verifying Party     : IESG